Mazda B-Series 1998-06

Evaporative Emission Control (EEC) Systems

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Gasoline fuel is a major source of pollution, before and after it is burned in the automobile engine. From the time the fuel is refined, stored, pumped and transported, again stored until it is pumped into the fuel tank of the vehicle, the gasoline gives off unburned hydrocarbons (HC) into the atmosphere. Through the redesign of storage areas and venting systems, the pollution factor was diminished, but not eliminated, from the refinery standpoint. However, the automobile still remained the primary source of vaporized, unburned hydrocarbon (HC) emissions.

Fuel pumped from an underground storage tank is cool but when exposed to a warmer ambient temperature, will expand. Before controls were mandated, an owner might fill the fuel tank with fuel from an underground storage tank and park the vehicle for some time in warm area, such as a parking lot. As the fuel would warm, it would expand and should no provisions or area be provided for the expansion, the fuel would spill out of the filler neck and onto the ground, causing hydrocarbon (HC) pollution and creating a severe fire hazard. To correct this condition, the vehicle manufacturers added overflow plumbing and/or gasoline tanks with built in expansion areas or domes.

However, this did not control the fuel vapor emission from the fuel tank. It was determined that most of the fuel evaporation occurred when the vehicle was stationary and the engine not operating. Most vehicles carry 5-25 gallons (19-95 liters) of gasoline. Should a large concentration of vehicles be parked in one area, such as a large parking lot, excessive fuel vapor emissions would take place, increasing as the temperature increases.

To prevent the vapor emission from escaping into the atmosphere, the fuel systems were designed to trap the vapors while the vehicle is stationary, by sealing the system from the atmosphere. A storage system is used to collect and hold the fuel vapors from the carburetor (if equipped) and the fuel tank when the engine is not operating. When the engine is started, the storage system is then purged of the fuel vapors, which are drawn into the engine and burned with the air/fuel mixture.

Evaporative Canister





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Fig. Location of the evaporative canister near the firewall on the right side fender well-1994-95 MPV shown

The fuel evaporative emission control canister should be inspected for damage or leaks at the hose fittings. Repair or replace any old or cracked hoses. Replace the canister if it is damaged in any way. The evaporatve canister can be found in the following locations:



1994-95 MPV-right side rear of the engine compartment
 
1996-98 MPV-underneath the right side of the vehicle near toward the front
 
1994-97 B Series Pick-up and Navajo-left side radiator support, under the hood.
 
1998 B Series Pick-up-left side inner frame rail underneath the vehicle
 

Operation



Fuel vapors trapped in the sealed fuel tank are vented through the fuel vapor valve assembly in the top of the tank, or vent cut valve at the fuel tank filler tube. The vapors leave the valve assembly through a single vapor line and continue to the carbon canister for storage until they are purged to the engine for burning.

Purging the carbon canister removes the fuel vapor stored in the carbon canister. The fuel vapor is purged via a purge control solenoid or vacuum controlled purge valve. Purging occurs when the engine is at normal operating temperature and off idle.

The evaporative emission control system consists of the following components: fuel vapor (charcoal) canister, fuel vapor valve (Navajo and 1994-97 B Series Pick-up), fuel separator (MPV), cut valve (MPV), check valve (MPV), fuel vapor canister purge solenoid, pressure/vacuum relief fuel tank filler cap, as well as, the fuel tank and fuel tank filler pipe, vapor tube and fuel vapor hoses.

Canister Purge Solenoid


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Fig. Location of the canister purge solenoid on 1996-98 MPV models

The canister purge control solenoid is inline with the carbon canister and controls the flow of fuel vapors out of the canister. It is normally closed. When the engine is shut OFF , the vapors from the fuel tank flow into the canister. After the engine is started, the solenoid is engaged and opens, purging the vapors into the engine. With the solenoid open, vapors from the fuel tank are routed directly into the engine. The canister purge control solenoid can be found in the following locations:



1994-95 MPV-right side front of the engine compartment next to the radiator
 
1996-98 MPV-right side of the engine compartment against the firewall
 
1994-97 B Series Pick-up and Navajo-left side radiator support, under the hood
 
1998 B Series Pick-up-mounted on the fuel vapor canister
 

Evaporative Emissions Canister


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Fig. Evaporative canister and hose routing on the 2.3L engine 1994-97 B Series Pick-up



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Fig. Evaporative canister and hose routing on the 3.0L engine for 1994-97 B Series Pick-up



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Fig. Evaporative canister and hose routing on the 4.0L engine for 1994-97 B Series Pick-up and Navajo models



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Fig. Evaporative canister and hose routing for all 1998 B Series Pick-up engines-note location of the canister purge control solenoid



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Fig. Evaporative canister location-1994-95 MPV models



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Fig. Evaporative canister assembly-1996-98 MPV models

The fuel vapor canister is also referred to as evaporative emissions canister or charcoal canister.

The fuel vapors from the fuel tank are stored in the fuel vapor canister until the vehicle is operated, at which time, the vapors will purge from the canister into the engine for consumption. The fuel vapor canister contains activated carbon, which absorbs the fuel vapor. The fuel vapor canister can be found in the following locations:



1994-95 MPV-right side rear of the engine compartment
 
1996-98 MPV-underneath the right side of the vehicle toward the front
 
1994-97 B Series Pick-up and Navajo-left side radiator support, under the hood
 
1998 B Series Pick-up-left side inner frame rail underneath the vehicle
 

Fuel Vapor Valve

This component is also known as the evaporative emission valve on 1995-98 models.

Fuel vapor in the fuel tank is vented to the carbon canister through the vapor valve assembly. The valve is mounted in a rubber grommet at a central location in the upper surface of the fuel tank. A vapor space between the fuel level and the tank upper surface is combined with a small orifice and float shut-off valve in the vapor valve assembly to prevent liquid fuel from passing to the carbon canister. The vapor space also allows for thermal expansion of the fuel.

Pressure Vacuum Filler Cap

The fuel cap contains an integral pressure and vacuum relief valve. The vacuum valve acts to allow air into the fuel tank to replace the fuel as it is used, while preventing vapors from escaping the tank through the atmosphere. The vacuum relief valve opens after a vacuum of approximately-0.25 psi (1.7 kPa). The pressure valve acts as a backup pressure relief valve in the event the normal venting system is overcome by excessive generation of internal pressure or restriction of the normal venting system. The pressure relief is approximately 2 psi (14 kPa). Fill cap damage or contamination that stops the pressure vacuum valve from working may result in deformation of the fuel tank.

Removal & Installation



Canister Purge Solenoid Valve
  1. If on the 1998 B Series Pick-up, raise and safely support the vehicle.
  2.  
  3. Disconnect the vapor hoses from the canister purge control solenoid.
  4.  
  5. Unplug the electrical connector from the purge solenoid.
  6.  

The canister purge control solenoid is either secured into place with screw(s), or clipped onto a mounting bracket.

  1. Remove the purge solenoid valve from the vehicle.
  2.  

To install:

  1. Install the purge solenoid, then attach the engine wiring harness connector to the solenoid.
  2.  
  3. Connect the vapor hoses to the solenoid.
  4.  
  5. If on the 1998 B Series Pick-up, lower the vehicle.
  6.  

Evaporative Emission Canister

The fuel vapor canister is also referred to as evaporative emissions canister or charcoal canister.

  1. If the fuel vapor canister is mounted underneath the vehicle, raise and safely support the vehicle.
  2.  
  3. Disconnect the vapor hoses from the canister.
  4.  
  5. Remove the mounting screws, then remove the canister.
  6.  

To install:

  1. Position the canister in place, then install the mounting screws.
  2.  
  3. Attach all of the vapor hoses to the canister.
  4.  
  5. If the vehicle was raised, lower it to the ground.
  6.  

Fuel Tank Vapor Valve

This component is also known as the evaporative emission valve on 1995-98 models.

  1. Disconnect the negative battery cable.
  2.  
  3. Relieve the fuel system pressure.
  4.  
  5. Remove the fuel tank.
  6.  
  7. Remove the fuel vapor valve from the fuel tank by rotating the valve counterclockwise.
  8.  

To install:

  1. Install the fuel vapor valve into the fuel tank and secure it by rotating it clockwise.
  2.  
  3. Install the fuel tank in the vehicle.
  4.  
  5. Connect the negative battery cable.
  6.  

Pressure/Vacuum Relief Fuel Tank Filler Cap
  1. Unscrew the fuel filler cap. The cap has a pre-vent feature that allows the tank to vent for the first 3 / 4 turn before unthreading.
  2.  
  3. If equipped, remove the screw retaining the fuel cap tether and remove the fuel cap.
  4.  

To install:

  1. If equipped, position the end of the tether against its mounting boss, then install and tighten the tether screw.
  2.  
  3. Thread the filler cap into the fuel tank filler tube, making sure to turn it clockwise until the ratchet mechanism gives off 1-3 loud clicks.
  4.  

Testing



Canister Purge Solenoid Valve
  1. Remove the canister purge control solenoid.
  2.  
  3. Measure the resistance between the two solenoid terminals.
    1. If the resistance is between 30-90 ohms, proceed to the Step 3.
    2.  
    3. If the resistance is not between 30-90 ohms, replace the solenoid.
    4.  

  4.  
  5. Attach a hand-held vacuum pump to the intake manifold vacuum side of the purge solenoid, then apply 16 in. Hg (53 kPa) of vacuum to the solenoid.
    1. If the solenoid will not hold vacuum for at least 20 seconds replace it with a new one.
    2.  
    3. If the solenoid holds vacuum, proceed to Step 4. Keep the vacuum applied to the solenoid.
    4.  

  6.  
  7. Using an external voltage source, apply 9-14 DC volts to the solenoid electrical terminals.
    1. If the solenoid opens and the vacuum drops, the solenoid is working properly.
    2.  
    3. If the solenoid does not open and the vacuum remains, replace the solenoid with a new one.
    4.  

  8.  

Check Valve

The check valve is also referred to as the two-way check valve.



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Fig. Vacuum port identification for testing the check valve

  1. Remove the check valve and blow air through port B and check that the air flows smoothly through port C .
  2.  
  3. Blow air into port C and check that the air flows smoothly through port A .
  4.  
  5. Replace the valve as required.
  6.  

Cut Valve


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Fig. Location of cut valve vacuum port A

  1. Remove the cut valve from the vehicle.
  2.  
  3. While holding the valve in the horizontal position, blow air into port A and verify that their is air flow through the valve.
  4.  
  5. Next, hold the valve in the tilted position and blow air through port A again.
  6.  
  7. Verify that air does not flow through the valve.
  8.  
  9. If not as specified, replace the cut valve.
  10.  

Evaporative Emissions Canister

The fuel vapor canister is also referred to as evaporative emissions canister or charcoal canister.

Generally, the only testing done to the vapor canister is a visual inspection. Look the canister over and replace it with a new one if there is any evidence of cracks or other damage.

Do not try to check the fuel saturation of the canister by weighing it or by the intensity of the fuel odor from the canister. These methods are unreliable and inhaling gasoline fumes can be toxic.

Servicing

The evaporative and emission components are designed and tested to exceed 120,000 mi. (193,116km) or 10 years of vehicle use. No maintenance or service should be required, except in the case of damage or malfunction. If either condition should exist, simply replace that component.

 
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